1. Field of the Invention
This invention relates to polyester resins and more particularly to a method for producing a light-colored unsaturated polyester resin containing at least 2% by weight of bromine by reacting polyols or alkylene oxides with polycarboxylic acids or anhydrides. Such bromine-containing unsaturated polyester resins exhibit improved fire resistance characteristics.
2. Description of the Prior Art
One means for introducing bromine into unsaturated polyester resins is to employ dibromo neopentyl glycol as one of the polyol ingredients of the resin. Typical unsaturated polyester resins which have employed dibromo neopentyl glycol in the past have exhibited darkened colors when fabricated in glasslined equipment and even darker colors when fabricated in stainless steel equipment. The objectionable color can be attenuated to some extent by dissolving the bromine-containing unsaturated polyester resin in, for example, styrene to form the usual polyester resin syrup. It is also known to add small quantities of an epoxide such as butylene oxide or epichlorohydrin to the resin syrup to lighten further the dark colored resin syrup. It has also been proposed to include triphenyl phosphite in the ingredients for the polyester reaction with a view to mitigating the dark color of the resultant resin.